Question

1)List 3 proteins found in hen egg white and state their functions

2)Will brown egg white have the same protein composition as white egg white? Provide suitable justifications for your answer.

3) What is size exclusion chromatography? How does it separate small vs large proteins?

Answer 1

1. Three proteins found in hen egg white are Ovalbumin, ovomucoid and lysozyme. Ovalbumin content is a 45 kDa protein which is 54% of the total protein content. It is a glycoprotein, which is mainly used for storage and transport of metal ions. It also provides nutrition to the growing embryo after fertilization. It can react with various proteases and thereby act as substrates for them.

Ovomucoid is also a glycoprotein of 28 kDa molecular weight. It is a trypsin inhibitor present in egg white, with one molecule capable of binding 3 trypsin molecules. It is also the major allergen responsible for IgE mediated allergic reactions. It comprises of 11% of total egg white protein content. It inhibits bacterial proteases, thereby protecting the embryo against bacterial growth.

Lysozyme has a molecular weight of 14.4 kDa and comprises 3.5% of total egg white protein content. It can hydrolyze the beta bond between N-acetylneuraminic acid and N-acetylglucosamine occurring in the bacterial cell wall. Thus, it prevents bacterial growth. It is positively charged and can bind negatively charged ovomucoid protein. It is also a nutrient during early embryonic growth.

2. The color of eggs shell depends on the breed of chicken they are derived from. Their protein content remains the same. All egg whites have 4 gram protein, irrespective of the color of the egg shell. Brown eggs are costlier as the chicken that produce them are bigger in size. Brown eggs are slightly richer than white eggs in omega-3 fatty acids. There have been reports that two ovalbumin related protein OVAX and OVAY are present in larger amounts in brown eggs as compared to white eggs. However, there is protein composition between white and brown egg white is mostly the same.

3. Size exclusion chromatography is a chromatographic technique that separates protein based on size when they move through a resin. The resin consists of porous spherical particles forming a matrix. Depending on pore sizes, larger molecules cannot pass through the pores and are therefore hindered. Small proteins can pass through the pores of the matrix and will move faster through the resin. Hence, smaller proteins are eluted out faster than larger proteins.